Microbiological Processes in Sediments

EPA Grant Number: R825433C038
Subproject: this is subproject number 038 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Microbiological Processes in Sediments
Investigators: Nelson, Douglas
Institution: University of California - Davis
EPA Project Officer: Packard, Benjamin H
Project Period: June 30, 1995 through June 30, 1998
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


The investigators are studying the microbiology of Hg methylation in Clear Lake sediments. It is important to thoroughly understand this process because methyl Hg is highly toxic and is the form of Hg that bioaccumulates throughout the food chain. Hg methylation appears to be carried out exclusively by microorganisms. Although many microorganisms have been shown to methylate Hg in pure culture, there is literature evidence that sulfate reducing bacteria (obligately anaerobic bacteria that use sulfate as a terminal electron acceptor) are potentially responsible for up to 95% of the Hg methylation in estuarine and freshwater environments. In addition, microbial processes in the upper few cm of sediments affect the mobilization of Fe, and P, elements of interest to other investigators at Clear Lake. The dependence of methylation on organic loading versus other factors, such as inorganic Hg and sulfate (SO4) concentrations, tests the idea that methylation is a multiple stress, arising from eutrophication in combination with Hg pollution.


To date the investigators studying methylation of Hg in sediments, have had to resort to studying the "potential rate of methylation". The qualifying word "potential" is necessitated by significant departures from in situ conditions including the following: (1) use of HgCl2 spikes which significantly increase the total inorganic mercury in the sediments and (2) slurrying of sediments to ensure uniform stimulation and/or a uniform specific radioactivity (if 203Hg is used). The very recent advances which make possible the use of higher activity 203Hg coupled with the very high inorganic Hg levels of Clear Lake suggest that it is the ideal place to try to measure in situ methylation rates in spatially structured cores injected at various depths with true tracer levels of 203Hg-HgCl2 (incubated in the lab underd conitions). These rates coupled in situ with an extension of the exciting recent preliminary findings on methylmercury evolution from similar structured cores suggest that a good mass balance model is a reasonable goal.

Expected Results:

In the literature on anaerobic sediments it is dogma that sulfate-reducing bacteria are the important methylators of mercury. The investigators use of molybdate in preliminary experiments suggests that concentrations which completely inhibit sulfate-reducing bacteria, stop only one-third to one-half of mercury methylation potential. Likewise long cores from Clear Lake show deep secondary maxima of methylmercury far below the depth of sulfate penetration.

The strong gradient of inorganic Hg in Clear Lake, and the variations in other parameters such as sulfate concentration and organic matter loading should result in a much better understanding of the microbial ecology of methylation. We can also compare the methylation process in Clear Lake with other systems under investigation by our group such as Davis Creek Reservoir and Coast Range and Sierra streams.

Supplemental Keywords:

Environmental monitoring, hydrology, mercury methylation, bioaccumulation, contaminated sediment, Clear Lake, eutrophication, mass balance model, aquatic ecosystem., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Ecology, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Contaminated Sediments, mercury transport, Aquatic Ecosystem, Ecology and Ecosystems, Watersheds, wetlands, mercury, food chain, migratory birds, watershed management, contaminated sediment, nutrient flux, esturarine eutrophication, fish consumption, wetland restoration, watershed influences, diagnostic indicators, lakes, mercury methylation, aquatic ecosystems, lake ecosysyems, mercury contamination in fish, wildlife bioaccumulation, environmental stress, riparian habitat, bioaccumulation

Progress and Final Reports:

  • 1995
  • 1996 Progress Report
  • Final

  • Main Center Abstract and Reports:

    R825433    EERC - Center for Ecological Health Research (Cal Davis)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
    R825433C002 Sacramento River Watershed
    R825433C003 Endocrine Disruption in Fish and Birds
    R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
    R825433C005 Fish Developmental Toxicity/Recruitment
    R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
    R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
    R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
    R825433C009 Modeling Ecosystems Under Combined Stress
    R825433C010 Mercury Uptake by Fish
    R825433C011 Clear Lake Watershed
    R825433C012 The Role of Fishes as Transporters of Mercury
    R825433C013 Wetlands Restoration
    R825433C014 Wildlife Bioaccumulation and Effects
    R825433C015 Microbiology of Mercury Methylation in Sediments
    R825433C016 Hg and Fe Biogeochemistry
    R825433C017 Water Motions and Material Transport
    R825433C018 Economic Impacts of Multiple Stresses
    R825433C019 The History of Anthropogenic Effects
    R825433C020 Wetland Restoration
    R825433C021 Sierra Nevada Watershed Project
    R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
    R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
    R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
    R825433C025 Regional Movement of Toxics
    R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
    R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
    R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
    R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
    R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
    R825433C031 Pre-contact Forest Structure
    R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
    R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
    R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
    R825433C035 Border Rivers Watershed
    R825433C036 Toxicity Studies
    R825433C037 Watershed Assessment
    R825433C038 Microbiological Processes in Sediments
    R825433C039 Analytical and Biomarkers Core
    R825433C040 Organic Analysis
    R825433C041 Inorganic Analysis
    R825433C042 Immunoassay and Serum Markers
    R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
    R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
    R825433C045 Microbial Community Assays
    R825433C046 Cumulative and Integrative Biochemical Indicators
    R825433C047 Mercury and Iron Biogeochemistry
    R825433C048 Transport and Fate Core
    R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
    R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
    R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
    R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
    R825433C053 Currents in Clear Lake
    R825433C054 Data Integration and Decision Support Core
    R825433C055 Spatial Patterns and Biodiversity
    R825433C056 Modeling Transport in Aquatic Systems
    R825433C057 Spatial and Temporal Trends in Water Quality
    R825433C058 Time Series Analysis and Modeling Ecological Risk
    R825433C059 WWW/Outreach
    R825433C060 Economic Effects of Multiple Stresses
    R825433C061 Effects of Nutrients on Algal Growth
    R825433C062 Nutrient Loading
    R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
    R825433C064 Chlorinated Hydrocarbons
    R825433C065 Sierra Ozone Studies
    R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
    R825433C067 Terrestrial - Agriculture
    R825433C069 Molecular Epidemiology Core
    R825433C070 Serum Markers of Environmental Stress
    R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
    R825433C072 Molecular Monitoring of Microbial Populations
    R825433C073 Aquatic - Rivers and Estuaries
    R825433C074 Border Rivers - Toxicity Studies